This invention relates to a device and method for longitudinally interfolding webs and, more particularly, to partially superposed webs. This invention has particular utility in providing interfolded facial tissues which are boxed so that as one tissue is removed, another tissue automatically appears.
For many years, the sequentially appearing tissues were manufactured in accordance with U.S. Pat. No. 2,626,145 wherein a pair of webs were transversely severed and interfolded -- and in many areas of the world where production capacity is not critical, this procedure is still used. However, in the more industralized areas, the demand for interfolded tissues was sufficiently great to justify more elaborate installations which used the longitudinally folding technique.
The first approach to longitudinal folding is described in U.S. Pat. No. 2,642,279. Although this was superior in productive capacity to the previously employed transverse folding technique, certain of the folding devices were cumbersome. These operated on the principle of completing the interfold of a pair of webs and thereafter unfolding the top web to insert another web edge. It was found more expedient to create a spacing between the two bottom plies of a web stack and insert therein an edge portion of another web -- this technique being described in U.S. Pat. No. 3,066,932.
The technique of the '932 patent has been used widely by one manufacturer notwithstanding the fact that it required right and left hand folding devices and the concomitant drawbacks of requiring extensive space and difficulty of threading and alignment. Further refinements have been advanced to the '932 patent technique (as in U.S. Pat. No. 3,291,479) but without altering the principle of using right and left hand folding devices.
Very early in the commercial utilization of the longitudinal interfolding technique, it was realized that substantial advantages could be achieved through the use of folding devices which operated on two webs simultaneously, i.e., eliminating the need for left and right hand folding boards and a simplified threadup procedure. One such approach is set forth in U.S. Pat. No. 3,199,861 which achieved interfolding by using the same handed interfording boards but required pre-folding plates for each web, therefore requiring the use of three forming positions for each two webs.
Another early approach is set forth in U.S. Pat. No. 3,285,599 which was commercially employed in a mill in Canada. In practice, threadup of these folding devices was difficult and time consuming because of the limited spacing between double-biased folding edges and the proximity of the guide. Prior to expansion of its operations into the United States, the patent company of the same manufacturer developed second and third approaches to interfolding. The second approach is according to teachings of U.S. Pat. Nos. 3,472,504 and 3,542,356 which involve a first folding plate which handled two superimposed webs to complete one longitudinal web fold and a partial longitudinal web fold on the opposite side, with the completion of the fold in a succeeding downstream second folding device.
The third approach, according to U.S. Pat. No. 3,841,620, returned to the method of using alternate left and right hand folding devices and was the method employed in the U.S. expansion mill operation. Thereafter, the machine in Canada was similarly altered.
The art therefore appreciated the advantages of a single design forming plate and had many available craftsmen and designers (or artisans and engineers, etc.) skilled in the art who could have realized these advantages -- but none did, and more importantly, these advantages were not reflected in any machine and process which has been reduced to practice. The instant invention does achieve these advantages through the use of a novel forming plate and method of operation.
It is appreciated by those skilled in the art that threading of a longitudinally interfolding machine can be a most vexing problem. Where 200 webs must be unrolled from parent rolls axially aligned along one side of the machine, taken over turning bars and thereafter threaded through right and left hand folding devices, it will be immediately appreciated that anything that allows sequential threadup of each pair of webs while running at a slow speed and simplifies this operation is indeed desirable. This is particularly the case where the rolls are usually mounted on driven unwind stands so that any web not immediately threaded causes considerable waste which is not only costly in terms of product, but can create a hazard in the mill.
The construction of the inventive folding plates significantly facilitates the threading operation as well as providing a reliable, foolproof interfolding. The novel structure responsible for these operational advantages, as well as permitting the saving of space, simplification of mechanism and significantly decreasing the problems of alignment, includes two sets of folding edges, each set extending from a point on the margin of the interfolded web path but with the significant difference from what has gone before in providing that one free edge of partially superposed webs is simultaneously and completely folded under the posed webs is simultaneously and completely folded under the superposed portion of the webs while the other is completely folded over this superposed portion.
Other objects and advantages of the invention may be seen in the details of construction and operation set down in the ensuing specification.